JP6001796B2 - Copper powder, method for producing the same, and conductive composition containing the same - Google Patents

Description

  The present invention relates to copper powder. Moreover, this invention relates to the manufacturing method of copper powder, and the electroconductive composition containing it.

  Copper powder is used to achieve electrical continuity between the external electrode of the electronic device and the printed wiring of the printed wiring board. It is also used for a conductive paste for an interlayer connection material that fills a wiring layer of a printed wiring board, a through-through hole provided in a multilayer printed wiring board, a via that is a non-through hole, or the like. In addition, copper powder is used in various applications such as conductive paste used for EMI shielding and electronic device connection, wiring paste for ceramic fired electronic parts such as capacitors and alumina substrates, etc. Appropriately shaped copper powder is used.

  The copper powder is usually used in the form of a conductive composition mixed with a binder resin or an organic solvent, for example, in the form of a conductive paste. The conductivity of the conductor formed from the conductive composition depends on the proportion of the copper powder contained in the conductive composition. Even when the same proportion of copper powder is contained, the shape of the copper particles Affects the conductivity of the conductor. For example, in the case of copper powder composed of spherical copper particles, the conductivity of the conductor is greatly influenced by the content ratio of the copper powder, and it is not easy to increase the conductivity unless the content ratio of the copper powder is increased. In contrast, copper powder made of dendritic copper particles is less affected by the content of copper powder on the conductivity of the conductor than spherical particles. In other words, the conductivity of the conductor is unlikely to depend on the content ratio of the copper powder. This is because dendritic copper particles have more contact points between particles than spherical copper particles. However, dendritic copper powder is not easy to be contained in a high content ratio in the conductive composition due to the low tap density. Further, dendritic copper powder is strongly aggregated and it is not easy to prepare a conductive composition with good dispersibility, and it is not easy to reduce the thickness of a conductor film formed from the conductive composition. Furthermore, it is difficult to fill the inside of a small diameter via, and it is difficult to cope with fine wiring.

  In addition to spherical and dendritic copper powder, rod-shaped copper powder is also known. For example, Patent Document 1 describes a rod-shaped copper powder obtained by crushing dendritic copper powder. In this copper powder, crushed pieces generated by crushing dendritic copper powder are aggregated to form a rod-like shape.

US5409520A

  Since the bar-shaped copper particles described in Patent Document 1 are agglomerated pieces as described above, since the tap density is high and the primary particles are coarse, the content ratio of the copper powder is increased similarly to the spherical copper particles. Otherwise, it is not easy to increase the conductivity of the conductor. In addition, since the average particle size is a relatively large particle size of around 10 μm, it is not easy to reduce the thickness of the conductor film, it is not easy to fill the inside of a small diameter via, and it is easy to form a pattern of fine wiring Not.

  Therefore, the object of the present invention is to improve the copper powder. Specifically, the conductivity of the conductor is less dependent on the content of the copper powder, the conductor film can be easily thinned, and the filling property in a small-diameter via is easy. It is desirable to provide a copper powder that is good and can easily form a fine wiring pattern.

The present invention, copper particles, or Ri Do on the surface of the copper core of particles metal other than copper is coated, the length of the length / short side of the long side at the minimum rectangle circumscribed to the projected image of the primary particles A copper powder containing 35% or more of particles having a rod-like shape with a value of 3 or more and 20 or less on a number basis ,
The projected area equivalent circle diameter obtained by image analysis of the primary particles is 0.1 μm or more and 4.0 μm or less,
The present invention provides a copper powder having a shape factor value of 1.8 or more and 3.5 or less by image analysis of primary particles defined by [maximum diameter × maximum diameter × π ÷ (4 × projected area)].

Moreover, the present invention is a copper powder comprising copper particles or particles formed by coating a metal other than copper on the surface of a copper core material,
When the powder density when an actual load of _0.63 kN is applied to an area of 20 mmΦ is ρ _0.63 and the powder specific resistance at that time is R _0.63 , the value of ρ _0.63 is 3. A copper powder having a value of 0 g / cm ³ or more and 5.0 g / cm ³ or less and an R _0.63 value of 9.0 × 10 ⁻¹ Ωcm or less is provided.

Furthermore, the present invention is a copper powder comprising copper particles or particles formed by coating a metal other than copper on the surface of a copper core material,
The specific resistance of the conductive film formed from 100 parts by mass of the copper powder and 10 parts by mass of resin is defined as R _10, and the ratio of the conductive film formed from 100 parts by mass of the copper powder and 15 parts by mass of resin. when the resistance was _{R 15,} the value of _{R 10} is not more than 1 × ^{10 -4} _Ωcm, in which the value of R 15 _{/ R 10} to provide a copper powder is 10 or less.

FIG. 1 is a schematic diagram showing a copper powder as a raw material for the copper powder of the present invention, and a schematic diagram showing a process for producing the copper powder of the present invention from the raw material copper powder. 2 is a scanning electron microscope image of the raw material copper powder used in Example 1. FIG. FIG. 3 is a scanning electron microscope image of the copper powder obtained in Example 4. FIG. 4 is a filled image of particles created based on the microscopic image shown in FIG.

  Hereinafter, the present invention will be described based on preferred embodiments thereof. The copper powder of the present invention consists of copper particles or particles in which the surface of the copper core material is coated with a metal other than copper. The copper powder of the present invention comprises these particles, and in some cases contains a trace amount of inevitable impurities. Moreover, you may contain powder other than copper powder etc. as needed. Hereinafter, unless otherwise specified, these particles are collectively referred to simply as “copper particles” for convenience.

  The copper particles constituting the copper powder of the present invention preferably have a projected area equivalent circle diameter of 0.1 μm or more and 4.0 μm or less, and 0.3 μm or more and 3.5 μm or less obtained by image analysis of the primary particles. Is more preferably 0.5 μm or more and 3.0 μm or less. Thus, the copper particles in the present invention belong to the category of fine particles. By setting the particle size of the primary particles within this range, the conductive film formed using the copper powder of the present invention can be thinned. At the same time, the copper powder of the present invention can be successfully filled into small-diameter vias, for example, small-diameter vias having a maximum diameter of 10 μm or more and 50 μm or less. Furthermore, high conductivity can be obtained. In contrast, for example, copper powder made of copper particles having a dendritic shape is very difficult to fill into a small-diameter via due to the large particle size of the copper particles. The projected area equivalent circle diameter is also called the Heywood diameter and is the diameter of a circle having the same area as the projected area of the particles. The projected area equivalent circle diameter is measured for 20 or more particles, and the arithmetic average value is taken as the measured value.

The copper particles constituting the copper powder of the present invention have a shape factor value of 1.8 or more and 3.5 by image analysis of primary particles defined by [maximum diameter × maximum diameter × π ÷ (4 × projected area)]. Preferably, it is 1.9 or more and 3.3 or less, more preferably 2.0 or more and 3.0 or less. As for the shape factor, 1 is the minimum value. When the shape factor is 1, the projected shape of the particle is a circle, and as this value increases from 1, the particle becomes gradually elongated. Therefore, the fact that the shape factor of the copper particles constituting the copper powder of the present invention is within the above range means that the copper particles have an elongated rod shape. When the value of the shape factor is in the above range, the conductive composition can maintain high conductivity that is not easily dependent on the ratio of the copper powder contained therein, and the conductive composition is prepared. Sometimes it is possible to obtain rigid rod-like particles in which copper particles are less likely to break. For the shape factor, the maximum diameter and projected area of any 20 or more individual particles are measured, the shape factor of each particle is obtained based on them, and the arithmetic average value is used as the measured value. The maximum diameter is the maximum projected diameter of the particle, and specifically refers to the length of the long side of the minimum rectangle circumscribed by the projected image of the primary particle. Needless to say, when calculating the shape factor based on the above formula, it is necessary to match the unit of the maximum diameter with the unit of the projected area (for example, when the unit of the maximum diameter is μm, The unit is μm ² ).

  In the present invention, it is desirable to more accurately represent the shape of the copper particles constituting the copper powder of the present invention by a combination of two or more parameters relating to the shape of the particles. From this viewpoint, the copper particles constituting the copper powder of the present invention have a shape factor value in the above-described range, and a projected area equivalent circle diameter / circular ellipse equivalent diameter value of 0.40 or more and 0. Is preferably .65 or less, more preferably 0.42 or more and 0.63 or less, and still more preferably 0.45 or more and 0.62 or less. Similarly to the shape factor described above, the value of the projected area equivalent circle diameter / circumferential ellipse equivalent diameter is also an index of the shape of the particle, and 1 is the maximum value. When this value is 1, the projected shape of the particle is circular, and as the value decreases from 1, the particle becomes increasingly elongated. Therefore, the value of the projected area equivalent circle diameter / circumferential ellipse equivalent diameter in the copper particles constituting the copper powder of the present invention within the above-mentioned range means that the copper particles have an elongated rod-like shape. ing. When the value of “projected area equivalent circle diameter / circumferential ellipse equivalent diameter” is within a predetermined range, high conductivity that is not easily dependent on the copper powder content in the conductive composition can be maintained, and paste processing can be performed. Sometimes it can be a rigid rod-like particle with few breaks. The projected area equivalent circle diameter / circumferential ellipse equivalent diameter value is a value obtained by measuring the projected area equivalent circle diameter / circumferential circle equivalent diameter value for any 20 or more individual particles, and calculating the arithmetic average value thereof. And The circumference equivalent circle diameter is the diameter of a circle having the same circumference as the circumference of the particle.

  The projected area, projected circumference, and projected maximum diameter of the particles, which are the basis for calculating the parameters described so far, are based on the electron microscopic image of the copper powder of the present invention, and the individual particles are filled by visual inspection of the operator. This is determined by binarization software analysis using the filled image. When multiple particles overlap in the observation field of view, the overlapping particles are virtually separated into individual particles by visual inspection of the operator, and an outline is taken for each separated particle. An image that has been binarized after being painted black is created. For the software analysis, for example, calculation can be performed by automatic analysis using image analysis type particle size distribution software Mac-VIEW which is computer software available from Mountec Co., Ltd.

  As described above, the copper particles constituting the copper powder of the present invention have a substantially rod shape. The copper powder of the present invention preferably contains 35% or more of copper particles having such a substantially rod-like shape on a number basis, and the inclusion of 60% or more is a viewpoint of stabilizing the conductive performance with respect to the copper powder content. Is preferable. This ratio is obtained by observing the copper powder of the present invention with an electron microscope, and measuring the number of particles having a projected area equivalent circle diameter / circular ellipse equivalent diameter satisfying the above range for any 20 or more particles. It is obtained by calculating the proportion of the total number of particles. Here, “substantially rod-like” means that the value of the length of the long side / the length of the short side in the minimum rectangle used when obtaining the maximum diameter is preferably 3 or more and 20 or less, more preferably 3 The shape which is 15 or less is said.

The copper powder of the present invention comprising copper particles having a substantially rod-like shape is bulky due to the rod-like shape of the copper particles. In contrast, since copper powder made of copper particles having a spherical shape is closely packed, when compared with the same mass, the bulk is lower than the copper powder of the present invention, and the conductive performance varies. It will be easy. Moreover, when compared with the same mass, the copper powder composed of the dendritic copper particles becomes too bulky than the copper powder of the present invention, and the aggregation between the particles becomes strong. Specifically, the copper powder of the present invention preferably has a value of ρ _0.63 when the powder density when an actual load of _0.63 kN is applied to an area of 20 mmΦ is ρ _0.63 . It is 0 g / cm ³ or more and 5.0 g / cm ³ or less. Within this range, sufficient conductivity can be achieved when the conductive paste is made even at a low concentration, and the dispersibility in the resin can be high. From the above viewpoint, the value of ρ _0.63 is more preferably 3.1 g / cm ³ or more and 4.7 g / cm ³ or less, and still more preferably 3.3 g / cm ³ or more and 4.3 g / cm ^3. cm ³ or less.

Moreover, the copper powder of the present invention has a low powder resistance even in a low compression state due to the rod-like shape of the copper particles. In contrast, copper powder composed of spherical copper particles makes it easy to reduce the powder resistance sufficiently in the low compression state due to the small number of contact points between the particles. Instead, it shows low resistance only when it is in a highly compressed state. Specifically, the copper powder of the present invention preferably has a value of R _0.63 of R _0.63 when the powder specific resistance when an actual load of _0.63 kN is applied to an area of 20 mmΦ is R _0.63. .0 × and the ^{10 -1} [Omega] cm or less, more preferably 5.0 × ^{10 -1 Ωcm} or less, or less and more preferably 5.0 × ^{10 -1 Ωcm.}

  Note that the measurement conditions for the above-mentioned powder density and powder specific resistance were set when an actual load of 0.63 kN was applied to an area of 20 mmΦ (circular shape with a diameter of 20 mm). When used as a body composition, copper particles must be in contact with each other to form a network of conductive paths even at a relatively low compressive stress level, such as the initial stage of curing of the composition. This is because the value used as the index is considered to correspond to the measurement condition of the present invention.

  The above-mentioned compact density and compact specific resistance are measured by the following method. 5 to 7 g of copper powder whose mass has been measured in advance is put into a probe cylinder having a diameter of 20 mm of the dust resistance measuring apparatus. The sample thickness and resistivity measuring instrument (4-probe method) when a load is gradually applied to the probe cylinder by a hydraulic jack is monitored. The dust resistance value is calculated from the sample thickness, the cylinder area, and the resistance value when a load is applied. On the other hand, the green density is calculated from the measured mass and the sample thickness. In the present invention, the dust density and the dust resistivity when the cylinder load is 0.63 kN are calculated. Specific examples of the device name include a dust resistance measurement system (Mitsubishi Chemical PD-41) and a resistance measurement device (Mitsubishi Chemical MCP-T600) mounted.

When the conductive composition is prepared by mixing the copper powder of the present invention with a binder resin, the resistance of the conductor formed from the conductive composition depends greatly on the content of the copper powder in the conductive composition. The resistance value can be kept low. That is, as a result of the study by the present inventors, it has been found that the conductivity of the conductor is less dependent on the content ratio of the copper powder. The reason for this is not because the copper powder of the present invention comprising copper particles having a substantially rod-like shape has anisotropy in the shape of the copper particles and can achieve low resistance even under a low load. The present inventor has guessed. In contrast, the copper powder composed of copper particles having a spherical shape ensures sufficient contact between the particles unless the copper powder is highly blended due to the isotropic particle shape. And the resistance of the conductor cannot be reduced. Specifically, in the copper powder of the present invention, when the specific resistance of the formed and a copper powder 100 parts by mass 10 parts by mass of the binder resin conductive film was R _10, the value of R ₁₀ is 1 × 10 It is preferably ⁻⁴ Ωcm or less, more preferably 8 × 10 ⁻⁴ Ωcm or less, and even more preferably 5 × 10 ⁻⁵ Ωcm or less. When the specific resistance of the conductive film formed from 100 parts by mass and 15 parts by mass of the binder resin is R ₁₅ , the value of R ₁₅ / R ₁₀ is preferably 10 or less, and 7 or less. Is more preferable and 5 or less is still more preferable.

  In the copper powder of the present invention, the copper particles themselves can be used as the particles constituting the particles, and the particles obtained by coating the surface of the copper core material with a metal other than copper (hereinafter referred to as “metal”). Also referred to as “coated copper particles”. Examples of the coating metal used for the metal-coated copper particles include silver, gold, platinum, tin, and nickel. Of these coated metals, it is particularly preferable to use silver, which is a noble metal that has high film-forming properties on copper and high conductivity and is relatively inexpensive. The coating metal may continuously cover the entire surface of the copper core without gaps, or may be partially coated so that the surface of the copper core is partially exposed. When the coated metal is, for example, silver, the ratio of the coated metal to the metal-coated copper particles is preferably 1% by mass or more and 30% by mass or less with respect to the mass of the metal-coated copper particles.

  As described above, the conductivity of a conductor formed using the copper powder of the present invention as a raw material is less dependent on the content ratio of the copper powder. This is advantageous in that when the conductor is produced by applying the conductive composition containing the copper powder of the present invention, the resistance of the conductor is less likely to vary even when uneven coating occurs. It is. In addition, when a conductive composition is filled in a via formed in a printed wiring board, generally, the binder resin is more preferentially filled in the via than the copper powder, and accordingly, the via is contained in the via. Although the composition of the filled conductive composition is likely to change, the use of the copper powder of the present invention can suppress the change in resistance of the conductive composition to a small level even when the composition is changed. .

The conductive film to be measured for the specific resistances R ₁₀ and R ₁₅ described above is prepared by the following procedure. As the binder resin, a liquid phenol thermosetting resin (PL-2243 manufactured by Gunei Chemical Industry Co., Ltd.) is used. This binder resin and the copper powder of the present invention are mixed at the above-mentioned ratio, and 5 parts by mass of NMP and 0.1 part by mass of a leveling agent (KF-352A manufactured by Shin-Etsu Silicone Co., Ltd.) are added as a solvent. Using a stirring deaerator (ARE-500, manufactured by Shinky Corporation), the mixture was temporarily mixed for 1 minute at a rotation speed of 1,000 rpm, and then charged in a three-roll mill (EXAKT M-80E). The conductive composition is obtained by further kneading five times under the conditions of a roll speed of 100 rpm and a gap between rolls of 10 μm. This conductive composition is coated on a glass plate using a glass epoxy resin plate applicator, and an applied body is first formed so as to have a thickness of 30 μm. The coated body thus obtained is fired to obtain a conductive film. The firing conditions are 1 hour at 160 ° C. in a nitrogen atmosphere.

A method for measuring the specific resistances R ₁₀ and R ₁₅ of the conductive film is as follows. The specific resistance is calculated from the film thickness of the conductive film left for 24 hours at 25 ° C. and 60% RH and the resistance value of the conductive film measured by the four probe method. Examples of the resistance measuring device include Loresta GP manufactured by Mitsubishi Chemical Analytech.

  Next, the suitable manufacturing method of the copper powder of this invention is demonstrated. The copper powder of the present invention is preferably made of a raw material having an irregular shape having a crushing starting point such as a “corner portion” or a “constriction portion” that is easily mechanically crushed as a particle shape. One feature is that the copper particles having a portion that can be generated by crushing, for example, copper powder composed of dendritic copper particles, are used as the raw material for the particles that are long in one direction. Furthermore, it has one of the features that the dendritic copper particles are crushed under specific conditions to obtain the target copper powder.

The dendritic copper particles as a raw material can be suitably produced by, for example, an electrolytic method. The dendritic copper particles preferably have a volume cumulative particle size D ₅₀ measured by a laser diffraction / scattering particle size distribution analyzer of 0.5 μm or more and 7.0 μm or less, and 1.0 μm or more and 6.0 μm or less. More preferably, it is 1.2 μm or more and 5.0 μm or less. In particular, when the copper particles are observed using a scanning electron microscope (hereinafter also referred to as “SEM”), it has one main shaft portion, and a plurality of branch portions branch obliquely from the main shaft, It has a dendritic shape that grows two-dimensionally or three-dimensionally, and the number of branch portions (number of branch portions / main shaft portion major axis L) with respect to the major axis L shown in FIG. 1 is 0.5 / μm or more. It is preferable to use those of 30.0 / μm or less, particularly 1.0 / μm or more and 25.0 / μm or less, particularly 3.0 / μm or more and 20.0 / μm or less. It is also preferable to use a material having a major axis L of 0.5 μm or more and 7.0 μm or less, particularly 1.0 μm or more and 6.0 μm or less, particularly 1.2 μm or more and 5.0 μm or less.

  When the copper powder containing dendritic copper particles used as a raw material is observed with a microscope at a magnification of 500 times or more and 20,000 times or less, the dendritic copper particles having the above-mentioned shape are 35% of the total copper particles. It is preferable to occupy at least several percent, particularly 60 percent or more.

  The copper powder containing dendritic copper particles used as a raw material can be suitably produced by, for example, an electrolytic method. As an electrolysis method, for example, an anode and a cathode are immersed in a sulfuric acid electrolytic solution containing copper ions, and a direct current is passed through the electrolyte to conduct electrolysis. A method of scraping and collecting by an electric method, washing with water, drying, and producing electrolytic copper powder through a sieving step and the like as necessary can be exemplified. In electrolysis, it is advantageous to add a small amount of chlorine to the electrolytic solution and scrape it off within a short time after deposition using an electrode having a predetermined surface roughness. The chlorine concentration of the electrolytic solution is preferably adjusted to 3 mg / L or more and 300 mg / L or less, particularly 5 mg / L or more and 200 mg / L or less. As for the surface roughness of the electrode, particularly the cathode, Rz specified in JIS B 0601-2013 is preferably 0.001 μm or more and 2.0 μm or less, particularly preferably 0.1 μm or more and 1.0 μm or less.

  The copper powder containing the above dendritic copper particles is crushed to produce the desired copper powder containing substantially rod-like copper particles. For crushing, it is preferable to employ a method in which excessive heat is not applied to the raw copper powder. From the viewpoint of preventing plastic deformation, it is also preferable to employ a medialess crushing method that does not use media such as beads and balls. A particularly preferred method is to force the slurry containing the raw material copper powder to pass through the narrow flow path under pressure, and in the dendritic copper particles as shown in FIG. In this method, the branch portion is crushed by bending and separating from the main shaft portion at the base portion. The diameter of the narrow channel is preferably about 100 μm to 300 μm. The applied pressure of the slurry is preferably 10 MPa or more and 100 MPa or less. Such forced passage can be performed once or multiple times. By performing the forced passage a plurality of times, it is possible to obtain a copper powder containing copper particles having a target shape and particle size. In addition, with the above constant apparatus conditions, as the crushing conditions, the work volume per unit volume of the slurry calculated from the capacity of the narrow flow path through which the slurry passes, the slurry pressure and the number of passes of the slurry batch are multiplied. Is preferably 200 J or more and 30,000 J or less. In particular, from the viewpoint of preventing an increase in resistance due to excessive atomization while maintaining a fine copper particle shape that exhibits low resistance even at low pressure, the work amount is particularly preferably 400 J or more and 25,000 J or less. . Examples of the apparatus capable of performing such operations include NanoVater from Yoshida Kikai Kogyo and NanoJet Pal from ordinary light.

  The above is a manufacturing method in the case where the copper particles are made of copper itself. However, when the copper particles are made of metal-coated copper particles, the following manufacturing method can be adopted. That is, first, core material particles made of copper are manufactured using the above-described method. Next, a coating metal is arranged on the surface of the obtained core material particles. As a method for arranging the coating metal, an appropriate method is adopted depending on the type of the coating metal. For example, when the coating metal is a metal nobler than copper, such as silver, a wet displacement plating method can be employed. Alternatively, a wet reduction plating method can be used.

  The copper powder of the present invention thus obtained is preferably used in the form of a conductive composition prepared by mixing with a binder resin or an organic solvent. Specific examples of the conductive composition include a conductive paste, a conductive ink, a conductive adhesive, and an EMI shield. These conductive compositions may be of a resin-curing type in which copper particles are pressure-bonded by curing of the resin to ensure conduction, or the organic components are volatilized by firing and the copper particles are sintered. It may be a fired mold that ensures conduction. In any type of conductive composition, the proportion of copper powder in the conductive composition is preferably 30% by mass to 98% by mass, and more preferably 35% by mass to 95% by mass. More preferably, it is 40 mass% or more and 90 mass% or less. Examples of other components contained in the conductive composition include binder resins such as various thermosetting resins such as epoxy resins and phenol resins, curing agents, curing catalysts, organic solvents, and glass frits. These components are blended at an appropriate ratio depending on the specific use of the conductive composition.

  Since the copper particles of the present invention are substantially rod-shaped, the number of contact points between the particles, when compared to spherical particles, even if the content ratio in the conductive composition is low, The resistance of the conductor can be lowered. Moreover, even if the non-uniform particle | grains generate | occur | produce at the time of application | coating of the electrically conductive composition containing this, the ratio of a copper powder and binder resin does not change easily, and the non-uniform | heterogenous resistance of a conductor hardly arises. It is difficult to change the ratio of the copper powder to the binder resin, which is also true for dendritic copper particles. However, dendritic copper particles are not easily reduced in particle size, It is difficult to fill a conductive composition containing copper particles into a small-diameter via. On the other hand, if the electroconductive composition containing the copper powder of the present invention consisting of substantially rod-like and fine copper particles is used, it can be successfully filled into a small-diameter via. Taking advantage of these advantages, the conductive composition containing the copper powder of the present invention is suitably used for, for example, electrical conduction between an external electrode of an electronic device and a printed wiring of a printed wiring board. Moreover, it is used suitably in order to form the printed wiring of a printed wiring board by a printing method.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the scope of the present invention is not limited to such examples.

[Example 1]
(1) Manufacture of dendritic copper particles In an electrolytic cell of 2.5 m × 1.1 m × 1.5 m (about 4 m ³ ), each of 9 pieces (1.0 m × 1.0 m) in size A Ti cathode plate (surface roughness Rz = 1.0 μm) and an insoluble anode plate were suspended so that the distance between the electrodes was 5 cm. A copper sulfate solution as an electrolytic solution is circulated at 300 L / min in the electrolytic bath, and an anode and a cathode are immersed in the electrolytic solution. Copper was deposited. The circulating electrolyte temperature was 40 ° C., the Cu concentration was 15 g / L, the sulfuric acid (H ₂ SO ₄ ) concentration was 200 g / L, and the chlorine concentration was 200 mg / L. The current density was adjusted to 100 A / m ² and electrolysis was performed for 30 minutes.
Copper deposited on the cathode surface was recovered by scraping with a scraper at a frequency of once every 30 seconds, and then washed to obtain a hydrous copper powder cake equivalent to 1 kg of copper powder. This cake was dispersed in 3 L of water to form a slurry, and then washed with pure water to remove impurities to obtain electrolytic copper powder. This electrolytic copper powder is referred to as “raw material copper powder A”. When the raw material copper powder A was observed by SEM, the major axis L of the major axis was 0.5 to 7.0 μm, and the number of branches / major axis major axis L was 0.5 to 30.0 / μm in the form of dendritic copper particles However, it was confirmed that it occupied 80% by number or more of all the copper particles. An SEM image of the obtained dendritic copper particles is shown in FIG.

(2) Manufacture of rod-shaped copper particle The target rod-shaped copper particle was manufactured by crushing the dendritic copper particle obtained by said (1). For the crushing, a Nanomizer NM2-2000AR, which is a high-speed shearing pulverizer from Yoshida Kikai Kogyo, was used. First, this was mixed with denatured alcohol to form a slurry so that the solid content of the dendritic copper particles was 30% by mass, and this slurry was put into the pulverizer and crushed. The operating conditions of the pulverizer were a slurry temperature of 20 ° C. or lower, a pressing force of 20 MPa, and a pass count of 100 (equivalent to a work amount of 10,000 J per unit slurry volume). Thus, the copper powder containing the target rod-shaped copper particle was obtained. When this copper powder was observed with an SEM, the projected area equivalent circle diameter obtained by image analysis of the primary particles was 0.1 μm to 4.0 μm, and the projected area equivalent circle diameter / circumferential ellipse equivalent diameter value was 0.40 or more. It was confirmed that the copper particles of 0.65 or less accounted for 35% by number or more of the total copper particles.

[Example 2]
In Example 1, the Cu concentration was 20 g / L and the current density was 200 A / m ² as the conditions for producing the copper powder of the raw material copper powder. Except for these, as in the case of the raw material copper powder A, a copper powder of dendritic copper particles was obtained. This copper powder is referred to as “raw material copper powder B”. Except this, it carried out similarly to Example 1, and obtained the copper powder containing the rod-shaped copper particle made into the objective.

Example 3
In Example 1, as a condition for producing copper powder of the raw material copper powder, an insoluble anode plate (DSE (manufactured by Permerek Electrode)) was used, the Cu concentration was 1 g / L, and the sulfuric acid (H ₂ SO ₄ ) concentration was 100 g. / L, the current density was 100 A / m ² , the amount of circulating fluid was adjusted to 5 L / min, and conditions for electrolysis for 20 minutes were adopted. Except for these, as in the case of the raw material copper powder A, a copper powder of dendritic copper particles was obtained. This copper powder is referred to as “raw material copper powder C”. The raw copper powder C was crushed under a pressure of 50 MPa and a pass count of 5 (equivalent to a work load of 1500 J per unit slurry volume). The rest was the same as in Example 1. Thus, the copper powder containing the target rod-shaped copper particle was obtained.

Example 4
Raw material copper powder C was used as the raw material copper powder. The crushing conditions were a pressure of 20 MPa and a pass count of 100 (equivalent to a work amount of 10,000 J per unit slurry volume). Except these, it carried out similarly to Example 1, and obtained the copper powder containing the rod-shaped copper particle made into the objective. The SEM image of the obtained copper powder is shown in FIG.

Example 5
Raw material copper powder A was used as the raw material copper powder. As the crushing conditions, first, a 100-pass treatment was performed at a pressure of 20 MPa, and then a 50-pass treatment (corresponding to a work volume of 23,000 J per unit slurry volume) was adopted at a pressure of 50 MPa. Except these, it carried out similarly to Example 1, and obtained the copper powder containing the rod-shaped copper particle made into the objective.

Example 6
Raw material copper powder C was used as the raw material copper powder. The crushing conditions were a pressure of 20 MPa and a pass count of 25 (equivalent to a work load of 2500 J per slurry unit volume). Except these, it carried out similarly to Example 1, and obtained the copper powder containing the rod-shaped copper particle made into the objective.

Example 7
The copper powder obtained in Example 6 was subjected to silver displacement plating to obtain a copper powder obtained by coating the surface of rod-shaped copper particles with silver.

[Comparative Example 1]
Wet spherical copper particles (Mitsui Mining & Smelting Co., Ltd. _{D 50} value 1.0 .mu.m) was used as Comparative Example 1.

[Comparative Example 2]
Wet plate-like copper particles (Mitsui Mining & Smelting Co., Ltd. _{D 50} value 5.2 .mu.m) was used as a comparative example 2.

[Comparative Example 3]
The raw material copper powder C used in Example 3 was used as Comparative Example 3 as it was.

[Comparative Example 4]
Example 1 of Patent Document 1 (Japanese Patent Laid-Open No. Hei 6-158103) related to the earlier application of the present applicant was re-examined, and the obtained copper powder was used as Comparative Example 4.

[Evaluation 1]
About the copper powder obtained by the Example and the comparative example, the projected area equivalent circle diameter was measured by image analysis. Image analysis type particle size distribution software Mac-VIEW was used as a measuring device. The measurement was performed on 20 or more particles, the projected area equivalent circle diameter was measured for each particle, and the arithmetic average value was calculated.
Moreover, about the copper powder obtained by the Example and the comparative example, the value of projected area circle equivalent diameter / circumference ellipse equivalent diameter was measured by the image analysis using the above-mentioned apparatus. The measurement is performed on 20 or more particles, and the projected area circle equivalent diameter and circumference equivalent circle diameter are measured for each particle, and the projected area equivalent circle diameter / circumferential circle equivalent diameter for each particle is determined from these values. A value was calculated, and an arithmetic average value of the value was further calculated.
Furthermore, about the copper powder obtained by the Example and the comparative example, the shape factor was measured by the image analysis using the above-mentioned apparatus. The measurement was conducted on 20 or more particles, the maximum projected diameter and the projected area were measured for each particle, the shape factor was calculated for each particle from these values, and the arithmetic mean value was calculated.
The above results are shown in Table 1 below. In each of the above measurements, based on the SEM image of the copper powder, the particles were visually filled, and image analysis was performed on the filled image. As an example, FIG. 4 shows a filled image corresponding to FIG. As is clear from the comparison between FIG. 3 and FIG. 4, when two or more particles are observed in FIG. 3, the particles are separated and painted in FIG. 4.

[Evaluation 2]
For copper powder obtained in Examples and Comparative Examples, the green density [rho _0.63 in the manner described above, was measured powder resistivity _{R 0.63} and resistivity _{R 10} and _{R 15} of the conductive film. These results are shown in Table 1 below.

[Evaluation 3]
For copper powder obtained in Examples and Comparative Examples were evaluated surface condition of the conductive film used for the measurement of the specific resistance R ₁₀ described above. Moreover, the filling property to the via | veer (diameter 50 micrometers) of the electrically conductive composition used for the measurement of the above-mentioned specific resistance was evaluated. These results are shown in Table 1 below.
[Surface properties of the conductive film]
The arithmetic average roughness (Ra) of the conductor film was measured using a surface roughness profile measuring device Surfcom 480B manufactured by Tokyo Seimitsu Co., Ltd. When the value was 1 μm or less, the surface property was judged as good (A), and when the value was 1 μm or more, it was judged as bad (B).
[Fillability of conductive composition into vias]
An insulating layer (thickness 50 μm) / ultra-thin copper foil layer (thickness 2 μm) / carrier copper foil layer (thickness 18 μm) is laminated on a laminated plate in which copper foils are laminated on both sides of a glass cloth insulating layer. Got. A CO ₂ laser was irradiated toward the surface copper foil on the substrate, and a bottomed via was formed from the carrier copper foil layer to the insulating layer. The maximum diameter of the opening of the bottomed via was 60 μm. In this way, a printed wiring board with a bottomed via was obtained. The bottomed via was filled with the conductive composition used for the measurement of the specific resistance R ₁₀ using a screen printer. Subsequently, the copper foil with a carrier was peeled off and cured at 160 ° C. for 1 hour in a nitrogen atmosphere to obtain a printed wiring board filled with a conductor inside the bottomed via. The cross section of the bottomed via portion of this printed wiring board was polished, and the obtained cross section was observed with a scanning electron microscope (magnification 1,000 times). Observe 10 bottomed vias, and if the void generation rate (void ratio) of 5 μm or more generated inside the bottomed via is 10% or less, it is judged as good (A), and the case where it is less than 10% is bad (B ).

As is clear from the results shown in Table 1, the conductor film formed from the conductive composition containing the copper powder obtained in each example has a low resistance, and the resistance is hardly affected by the amount of the copper powder, Furthermore, it turns out that the surface is smooth. Moreover, it turns out that this electroconductive composition has the favorable filling property to a small diameter via | veer.
On the other hand, when the copper powder consisting of the spherical copper particles of Comparative Example 1 is used, the resistance of the conductor film becomes higher than that of the example, and the resistance is easily affected by the amount of copper powder. . The same tendency as in Comparative Example 1 is observed for the copper powder composed of the flaky copper particles of Comparative Example 2. Using the copper powder of Comparative Example 3 that was used as it was without crushing the dendritic copper powder, the conductive composition could not be prepared due to the extremely low dispersibility. The copper powder of Comparative Example 4 lacked the ability to fill a small diameter via due to the large particle size.

  ADVANTAGE OF THE INVENTION According to this invention, the copper powder with which the electroconductivity of a conductor does not depend easily on the content rate of a copper powder is provided. In addition, according to the present invention, it is possible to provide a copper powder that is easy to reduce the thickness of the conductor film and has good filling properties in a small-diameter via.

Claims (8)

Copper particles, or copper other than copper metal on the surface of the core material is Ri Do of particles formed by coating, the length of the value of the length / short side of the long side at the minimum rectangle circumscribed to the projected image of the primary particles A copper powder containing 35% or more of particles having a rod-like shape that is 3 or more and 20 or less, based on the number of particles ,
The projected area equivalent circle diameter obtained by image analysis of the primary particles is 0.1 μm or more and 4.0 μm or less,
A copper powder having a shape factor value of 1.8 to 3.5 by image analysis of primary particles defined by [maximum diameter × maximum diameter × π ÷ (4 × projected area)].   2. The copper powder according to claim 1, wherein a value of projected area equivalent circle diameter / circumferential ellipse equivalent diameter obtained by image analysis of primary particles is 0.40 or more and 0.65 or less. When the powder density when an actual load of _0.63 kN is applied to an area of 20 mmΦ is ρ _0.63 and the powder specific resistance at that time is R _0.63 , the value of ρ _0.63 is 3. The copper powder according to claim 1, wherein the copper powder is 0 g / cm ³ or more and 5.0 g / cm ³ or less, and the value of R _0.63 is 9.0 × 10 ⁻¹ Ωcm or less. The specific resistance of the conductive film formed from 100 parts by mass of the copper powder and 10 parts by mass of resin is defined as R _10, and the ratio of the conductive film formed from 100 parts by mass of the copper powder and 15 parts by mass of resin. 4. The copper powder according to claim 1, wherein when the resistance is R ₁₅ , the value of R ₁₀ is 1 × 10 ⁻⁴ Ωcm or less, and the value of R ₁₅ / R ₁₀ is 10 or less. . The copper powder according to any one of claims 1 to 4 , wherein the particles having copper as a core material are particles in which silver is coated on a surface of a copper particle. 60% or more of particles having a rod-like shape having a long side length / short side length value of 3 or more and 20 or less in a minimum rectangle circumscribed by the projected image of the primary particles is included on a number basis. The copper powder according to any one of claims 1 to 5. Consists of copper particles, or particles in which the surface of the copper core is coated with a metal other than copper,
The projected area equivalent circle diameter obtained by image analysis of the primary particles is 0.1 μm or more and 4.0 μm or less,
A method for producing a copper powder having a shape factor value of 1.8 or more and 3.5 or less by image analysis of primary particles defined by [maximum diameter × maximum diameter × π ÷ (4 × projected area)] ,
A slurry of copper powder containing dendritic copper particles is forced to pass through a narrow channel under pressure, and the branching part of the dendritic copper particles is bent by the shearing force generated by the turbulent flow that occurs during passage. The manufacturing method of the copper powder which has the process to isolate | separate. The electroconductive composition containing the copper powder as described in any one of Claims 1 thru | or 6 .